You first have to make a roux. In a large pot, add the oil and flour and cook on medium high, constantly stirring for approximately 10 minutes until the roux is a golden tan color. Add the stock and stir until incorporated and it begins to thicken. Add the onion, celery, peppers, 2/3 of the sliced green onion and seasoning into the stock and simmer for 20 minutes. Add the shrimp to the sauce and cook for only about 2 minutes or until the shrimp turn pink. Serve over a mound of rice and add plenty of sauce. Garnish with the rest of the green onion. Etouffee means "smother," so don't skimp on the sauce!